The present invention relates generally to a sensor system to detect visibility and, more specifically, to a visibility sensor system having a removable sensor head that may be removed for servicing.
Reduced visibility on highways due to fog or blowing dust has often been the cause of tragic traffic accidents. Fog, especially in mountainous regions, has a tendency to build up in patchy dense pockets. At highway speeds, in particular, a driver may suddenly find himself within one of these patchy dense fog pockets.
The ability to adequately warn drivers of dense fog is highly desirable. If adequate warning is provided to drivers, drivers may then reduce their speed based on the density of the fog. Adequate warnings will reduce loss of life.
Several optical and non-optical methods for determining the presence of fog are known. Most, however, are not suitable for highway visibility sensors. There are several optical systems that may be used. Radar and lidar systems are used to gather general weather data. Such systems are too expensive, bulky, insensitive and difficult to use on a highway. Closed circuit television has limited use for visibility detection, but it cannot function at night and requires monitoring by an operator. Airports commonly use transmissometers. Transmissometers measure the transmission of a light beam traveling a given path. Transmissometers are very expensive and require considerable maintenance and thus are not suitable to detect patchy highway fog. Coulter counters are often used in clean room monitoring. Coulter counters are very expensive and have high maintenance and power consumption requirements.
Non-optical devices such as triboelectric current sensors depend on the flow of gas rubbing against an electrode. Fog, however, frequently occurs in quiet atmospheric conditions. Spark discharge sensors require sensor electrodes to continually be kept clean and thus maintenance costs are prohibitive. A dosimeter-type particle density measurement device does not provide real-time data.
Another optical device for measuring fog is a nephelometer. Known nephelometers have expensive optical systems and are very large in size. The optical system requires constant maintenance to clean the windows through which the optics are directed.
In certain situations, it may be desirable for the vehicle to have a visibility detection system associated therewith. It would likely be cost prohibitive to provide highway visibility detection systems across the country. Therefore, it is desirable to provide a visibility sensor system associated with the vehicle.
On ships, it is difficult to determine visibility due to lack of background for comparison. For ships, it may also be desirable to locate a visibility sensor on the ship.
It would therefore be desirable to provide a visibility sensor system that overcomes the drawbacks of the prior art. Particularly, it would be desirable to provide a visibility sensor system that is inexpensive, has low maintenance, and is reliable to endure the conditions experienced on a highway.